Method of recovering molybdenite



Sept- 3, 1963 G. E. ATwooD ETAL METHOD oF REcovERING MOLYBDENITE Filed Nov. 28, 1960 United States Patent 3,102,854 METHOD F RECOVERING MOLYBDENITE George E. Atwood and Charles H. Curtis, Tucson, Ariz.,

assignors to Duval Sulphur & Potash Company, Houston, Tex., a corporation of Texas Filed Nov. 28, 1960, Ser. No. 72,112 6 Claims. (Cl. 209-4) This invention relates to a method of recovering molybdenite from an aggregate containing other minerals, and more particularly to a method of varying the relative floatability of the several minerals and removing molybdenite by froth flotation. i

Molybdenite may be obtained from aggregate which includes other minerals such as iron and copper sulphide along with gangue material which usually is principally silica. Great difficulty is experienced in separating molybdenite from the aggregate as a high concentration product. It is also well known that Where the molybdenite containing aggregate has previously been separated from ore by a flotation process that the aggregate may be contaminated with reagents utilized in such flotation. These reagents should be preferably treated to render them ineffective in subsequent flotation.

The patent to Janney Resisue 22,117 suggests that the aggregate be heat treated to suppress the other minerals relative to the molybdenite and to render ineffective any reagents present from prior Iflotation processes. Reference is made to the Janney patent for a detailed discussion of the problems encountered, `types of reagents used, etc. However, the drying methods suggested by Janney result in loss of an important percentage of the molybdenite. In following the teaching of this patent either a low temperature may be used in which the suppression of copper and iron sulphides relative to molybdenite may not be sufficient to obtain a high concentration product, or a large percentage of the molybdenite will be lost as dust during the higher temperature drying procedure. The method of the Janney patent has been used continuously since the filing of the Janney application. This method `Works wel-l in cases Where atmospheric boiling temperatures are suicient to carry out the method. Where ternperatures greater than the atmospheric boiling point of the slurry are necessary, ldiflicult dust problems have been encountered. Although the industry has sought a way to eliminate the dust problem since the beginning of use of the Ianney method, the problem has remained unsolved. Also the industry has not been successful in providing a solution to the problem of local overheating in handling dry aggregate. Local overheating results in suppression of molybdenite.

It is an object of this invention to provide a method of increasing the floatability of molybdenite relative to other minerals in aggregate containing molybdenite in which high concentration molybdenite can the recovered without substantial loss of molybdenite.

Another object is to provide a method of increasing the floatability of molybdenite relative to other minerals in aggregate containing molybdenite by heat treating at a temperature in excess of the atmospheric `boiling point of the solution Without substantial loss of lmolybdenite.

Another object is to provide a method of increasing the floatability of molybdenite relative to other minerals in aggregate containing molybdenite by heat treating at a temperaturein excess of the atmospheric boiling point of the liquid phase of the slurry while maintaining the aggregate in slurry form to prevent dusting and loss of molybdenite.

Another object is to provide a method of increasing the floatability of molybdenite relative to other minerals in aggregate containing mo'lybdenite by heat treating at Gee temperatures in excess of the atmospheric boiling point of the liquid Vphase of the slurry in which local overheating of the molybdenite is prevented and excellent contact with air for oxidation is provided without substantial loss of molybdenite.

Another object of this invention is to reduce the. time that aggregate should be treated to render ineffective reagents used in prior flotation.

` Other objects, features and advantages of the invention will be apparent from the drawing, the specification and claims.

ln the drawing the single FIGURE is a schematic illustration of the method of this invention.

In accordance with this invention the molybdenite containing aggregate is heat treated at a temperature above the atmospheric boiling point of the liquid phase of the slurry and below a temperature at which substantial oxidation of the molybdenite will occur. This upper ternperature will normally be at about 550 F., but the molybdenite can be subjected to a temperature of Vabout 700 F. without substantial oxidation for a short period of time. This treatment renders ineffective reagents added to the aggregate during previous flotation procedures. By ineffective is meant, ineffective to substantially effect further flotation procedures. Also this treatment will effect oxidation of surfaces of minerals other than molybdenite decreasing their floatability. i

In accordance `with this invention, the aggregate is maintained in slurry form during the heat treating step. By slurry form is meant mixed with a solution such as water to form a slurry.

During the treating of the slurry it is maintained under a pressure substantially equal to the vapor pressure of the liquid phase of the slurry at the temperature at which treating is being carried out. By maintaining the pressure on the slurry at, at least7 substantially Kthe vapor pressure of the liquid phase of the slurry, the liquid phase of the slurry will be prevented from boiling away and the aggregate will be maintained in slurry form during treatment. Of counse, a higher pressure than the vapor pressure of the slurry could be utilized, but this higher pressure would be unnecessary and would not normally be utilized due to the utility cost in providing this high pressure.

It is preferred that the treatment be carried out at as low a temperature as practical to render ineffective the particular reagents used in previous dotation procedures to depress the fioatability of minerals other than molybdenite. This temperature will vary with the reagents used. Also the particular minerals involved may effect the ternperature needed to depress a particular reagent.

Preferably, the treatment is carried out in a vessel through -which steam `alone or with air is passed. As is -well known in the art, air provides #oxygen for oxidizing the reagents and surfaces of minerals other than molybdenite which tends to depress the floatability of minerals other than molybdenite. By passing this stream of steam with or without air upwardly through the body of slurry, constant agitation of the slurry is obtained. Where is not used excess steam is used to provide agitation. Due to constant movement of the particles of the slurry, formation of any hot spots in Jtheslurry is prevented and excellent contact -is obtained between the aggregate and steam and/or air, thus pnoviding for maximum efficiency.

After the slurry has been treated for the time and temperature desired to depress the oatabili-ty of minerals other than molybdenite, it is passed to flotation `cells wherein the molybdenite is removed from the ore With the conventional flotation procedures. The time as Well as temperature needed will depend on the reagents present. For instance, aggregate previously treated with Xanthate and methylamyl alcohol have been satisfactorily treated at a temperature of 300 F. under a pressure of 60' pounds feed will be provided by recycle from the flotation step after treatment through line X14. The feed may be thickened in thickener 9. From pump 13 the lfeed passes via line 15 `through a series of heat exchangers indicated generally at 16 `and 17. Also passing through these heat exchangers is the hot slurry leaving the treating vessel. The hot slurry `gives up a part of its heat to the incoming feed, thus pre-heating the feed for introduction into the vessel and lowering the vdischarge temperature below the flash point. At an appropriate spot in line 15 a surge chamber 18 is provided `to 'accommodate surges from l reciprocating pump `i3. The incoming feed from line 15 is continuously introduced into vessel 1.1 through inlet 119.

The slurry is Withdrawn `from the vessel 11 through outlet k21 from whence it passes through heat exchangers 17 and :16 to outlet line 22. From the outlet line 22' the treated slurry passes to a mixing stage 23 wherein it is aerated, Idiluted to flotation density `with cold water and reagent added. From stage 23 the slurry passes through line 24 to the flotation cells 25. The flotation cells 25 represent the conventional flotation procedure which, in

accordance with the usual practice, is preferably in several stages to obtain maximum recovery and grade of concentrate.

The slurry :level Within vessel 10 is determined by the controller indicated generally at 26. 'This controller is of the type having 1a pressure-sensing element 27 arranged vertically Labove a second pressure-sensing element 28. The normal slurry level is `above element 28 and below element 27. The controller 26 senses the difference in pressure from elements 27 and 2S and maintains a selected slurry level within the vessel 77 by controlling the outlet valve indicated :generally lat 29. From the description as it has thus .far proceeded, it will be `apparent that the aggregate is continuously fed to treatment vessel `12 and substantially continuously withdrawn through line 22. While the rate of withdrawal may vary from time to time, the withdrawal stream will be fairly constant.

Heat is provided for treating the slurry by steam introduced through line 31. In accordance with this invention, heat might be provided yfrom any other desired source.

Preferably, the steam volume is monitored by valve 32 to pass through the vessel 11 a selected volume of steam per hour.

`It will be noted that the steam pipe 31 connects to the top of the vessel 11. A continuation 31a of the steam pipe extends Idownwardly ythrough the vessel and terminatesV ladjacent the lower end of the vessel.

Air is introduced* int@ the vessel and preferably the air inlet conduit 33 connects rwith the steam pipe before itu enters the vessel. Inlhis manner, the .air is introduced with the steam near the bottom of the vessel.

As the air 'and steam pass upwardly through vessel `11 they will heat and .agitate the slurry. This agitation will provide for constant movement of the slurry particles and insure excellent contact between the slurry particles and the steam and air.

As the'hot steam is bubbling up through the slurry, both .the steam and slurry fwill constantly be in movement and the possibility of liot spots `which might occur with other forms of applying beat to the vessel is substantially removed.,

The `air in conduit 33 is pressurized by a suitable compressor not shown, and the volume of air introduced is regulated by la valve -indicated generally at 34. Instead of air an excess volume of steam may be used to provide agitation. Y

The slurry is maintained under a pressure which is at least substantially equal to thevapor pressure of the liquid phase of the slurry iby providing a pressure control valve 35 in the air and steam outlet conduit 36 in the top of vessel 11. A pressure-sensing controller indicated generally at 37 senses the pressure within the vessel 11 and controls the degree yof opening lof valve 3S tomaintain the desired pressure in ythe vessel.V Where 4a pressure of 60 pounds is maintained ton the vessel a temperature of about 300 F. can be obtained in the slurry. Preferably `the extent of boiling is limited to prevent boiling away the liquid phase of the slurry and drying ofthe aggregate. This has the two-fold advantage of retaining the aggregate in liquid form to permit it to be easily handled in a continuous process, and preventing loss of particles of the aggregate las dust entrained in ythe escaping air and vsteam which would occur if the slurry were permitted to dry out.

. From the above it will be appreciated that the objects of this invention have been attained. A method has been Y The process retainsv the molybdenite in slurry form for ease in handling and minimizing of loss of any of thev molybdenite. v

The foregoing disclosure and description of the invention is illustrative and explanatory thereof and various changes in the size, shape and materials, as well as in the details of the illustrated construction, may be made within the scope of the appended claims Without departing from the spirit of the invention.

What is claimed is:

1. The method of separating molybdenite from a mineral aggregate including molybdenite and other minerals such as iron and copper sulphides and gangue materials, said aggregatehaving been separated from ore by froth flotation, comprising, subjecting a slurry of said aggregate to a heating treatment at a temperature substantially in excess of the atmospheric boiling point of water and pressure at least substantially equal to the vapor pressure Y of the liquid phase of the slurry at saidV temperature to substantially depress the iloatability of the other minerals relative to that of lrnolybdenite, and then subjecting the aggregate to froth flotation and recovering the molybdenite therefrom. y

2. The method of separating molybdenite from a mineral aggregate including molybdenite and other minerals such `as iron and copper sulphides and gangueminerals, said aggregate having been separated from ore byrfroth flotation, comprising, subjecting a slurry of said aggregate to a heating treatment at a temperature substantially in excess of 212 F. and not more than approximately 700 F. while subjecting said slurry to a pressure at least substantially equal lto the vapor pressure of the liquid phase of the slurry at said temperature to substantially depress the floatability of the other minerals relative to that of molybdem'te, and then subjecting the aggregate Ato froth flotation and recovering the molybdenite therefrom.

3. The method of separating molybdenite from a mineral aggregate including molybdenite and other minerals such as iron and copper sulphides a-nd gangue minerals, said aggregate having been separated from ore by froth notation, comprising, subjecting a slurry of said aggregate to a heating treatment at a temperature substantially in excess of 212 F. and not more than 'approximately 550 1F. While subjecting said slurry to a pressure at least substantially equal to the vapor pressure of theliquid'r,

phase of the slurry at said temperature to substantially depress the oatability of the other minerals relative to that of -moly-bdenite, and t-hen subjecting the aggregate to froth =lotation and recovering the molybdenite therefrom.

4. The method of `separating molybdenite from a rnineral aggregate including molybdenite and other minerals such as iron and copper sulphides and gangue minerals, said aggregate having been separated from ore by froth flotation, comprising, continuously ltreating -a slurry of said aggregate, passing steam through said slurry, said steam being at a temperature substantially `in excess of the atmospheric boiling point of water and less than the temperature at which substantial oxidation of molybdenite occurs, maintaining a pressure on said slurry at least substantially equal to the vapor pressure of the liquid phase of said slurry to substantially suppress the iloatability of the other minerals relative to that of molybdenite, and then subjecting the aggregate to froth ilotation and recovering the molybdenite therefrom.

5. The method of separating molybdenite from a mineral aggregate including molybdenite and other minerals such as iron and copper sulphides and gangue minerals,

said aggregate having been separated from ore by frothv suppress the floatability of the other minerals relative to that of molybdenite, and then subjecting the aggregate to froth tlotation and recovering the molybdenite therefrom.

6. The method of separating molybdenite from a mineral aggregate including molybdenite and other minerals such as iron and copper sulphides and gangue minerals, said aggregate having been separated from ore by froth flotation, comprising, continuously treating a slurry of said aggregate, passing steam through said slurry, said steam being at a temperature substantially in excess of 212 F. and not more than 550 F., maintaining a pressure l011 said slurry at least substantially equal to the Vapor pressure of the liquid phase of said slurry to substantially suppress the oatability .of the other minerals relative to that of molybdenite, and then subjecting the aggregate Ito froth otation and recovering the molybdenite therefrom.

References Cited in the le of this patent UNITED STATES PATENTS Re. 22,117 Janney et al June 11, 1942 981,451 McKechnie Jan. 10', 1911 2,746,856 Mancke May 22, 1956 2,971,835 Matson Feb. 14, 1961 OTHER REFERENCES Germany, A22,891 VI/ 1A, Nov. 22,` 1950.4 Tsvetnye Metally, Vol. 32, No. 2, pages 10-13 (1959) (abstracted in Chem. Abstract 53 13924b). 

1. THE METHOD OF SEPARATING MOLYBDENITE FROM A MINERAL AGGREGATE INCLUDING MOLYBDENITE AND OTHER MINERALS SUCH AS IRON AND COPPER SUPLHIDES AND GANGUE MATERIALS, SAID AGGREGATE HAVING BEEN SEPARATED FROM ONE FORTH FLOTATION, COMPRISING, SUBJECTING A SLURRY OF SAID AGGREGATE TO A HEATING TREATMENT AT A TEMPERATURE SUBSTANTIALLY IN EXCESS OF THE ATMOSPHERIC BOILING POINT OF WATER AND LESS THAN THE TEMPERATURE AT WHICH SUBSTANTIAL OXIDATION OF MOLYBDINITE OCCURS WHILE SUBJECTING SAID SLURRY TO A PRESSURE AT LEAST SUBSTANTIALLY EQUAL TO THE VAPOR PRESSURE OF THE LIQUID PHASE IOF THE SLURRY AT SAID TEMPERATURE TO 